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TRN-4.02 - Residential Infills Policy

The City will install new lights on local service streets in residential areas at all intersections and at locations where the lighting levels may be below standard, as determined by the distance between the nearest two lights. If the distance is at, or greater than, the distances indicated in the table below based on luminaire/mast arm orientation, the light will be installed upon request or at staff initiative. Requests for infill lights on streets that are unimproved, or deteriorated to the point that they are nearly impassable, will be handled on a case-by-case basis; the policy is not to encourage travel at normal speeds on streets that are below standards.

LIGHT ORIENTATION

SPACING

Case I

295 feet

Case II

200 feet

Case III

175 feet

Case IV

225 feet

Case V

275 feet

w/cut-off

260 feet

Case VI

275 feet

w/cut-off

260 feet

Examples of each case of luminaire/mast arm orientation are attached .

BACKGROUND

The Street Lighting Standards adopted by the City Council (November 1984) are based on the ASCP and set minimum standards for street lighting using roadway classifications. The illumination standard for local service (residential) streets is that the intersections must be lighted and the average horizontal illumination between the lights be greater than or equal to 0.2 fc. In order to make this standard field expedient, calculations determined that the maximum distance between lights on a residential street that would still meet the standard was 295 feet. Therefore, if the distance between existing lights is greater than, or equal to, 295 feet, we would install a street light. Recent analysis has shown that the orientation of the luminaires has a dramatic effect on lighting levels and has required a reevaluation of a field expedient method to determine whether the City standard is met. The new method requires that we look at spacing and orientation.

If street lights are oriented over the same street, then a 295-foot spacing is acceptable; however, when other orientations exist, this spacing no longer works. In order to continue using spacing as a field calculation of the lighting level, the new policy will take into account the orientation of the luminaires as well as the space between them. This will ensure that lighting in residential areas will meet City standards.

These calculations of average horizontal illumination are based on computer modeling which takes into account street width, light type, mounting height, mast arm length, and other factors. The computer does not consider the presence of existing or future trees, the single largest source of interference with street lighting. The alternative to computer modeling would be time-intensive nighttime field measurements for each of the approximately 300 annual requests. Current field work is limited to a survey of the lights in the area and measurements between the lights near the area requested for infill.

The attached layouts (PDF document, 150 kb) show the different light orientations found in the City's system. Each of the six cases have a different light orientation. Case V and VI also consider the use of a cut-off lens, typically found on arterials, that reduces glare, but diminishes the spread of the light down the local service street.